Is it possible to create relational metabox values in a custom post?

Your question is focusing on the wrong thing. A metabox is just one way for a user to introduce some data. The more important question is how you should store that data in the database.

You could make ‘sport’ a custom post type and connect it to models using the Posts 2 Posts plugin. Then, for each connection, you can associate a ‘rank’ custom field:

https://github.com/scribu/wp-posts-to-posts/wiki/Connection-information

The plugin takes care of creating a metabox and of storing the values in an efficient manner.